This is my first post I am new in linux.I install debian 7 (wheezly) and then install iredmail-0.8.6.When i want to send an email with roundcube, it says: "SMTP Error (451): Failed to add recipient "postmaster@mydomain.com" (4.3.0 <postmaster@mydomain.com>: Temporary lookup failure"

------------------------------------------------------------------------------------------------------------------------------------why i have root@server1.mydomain.com , zharf@server1.mydomain.com ,postmaster@mydomainserver.com?Is it right?